A simple Python script to generate a web page worked perfectly under the shell account but failed with a 500 server error when I tried to see the web page though a browser (and thus the Apache server). It turned out that on shell.sonic.net, sys.version reports 2.7.5 (default, Apr 11 2018, 07:36:10) [GCC 4.8.5 20150623 (Red Hat 4.8.5-28)]